It is well known in the engine art to provide a compound multi-cylinder Otto cycle internal combustion engine which uses an exhaust-gas turbine to achieve additional engine power by some form of coupling to the output shaft. In an exhaust-gas turbocharger two turbo elements, a turbine and a compressor, are installed on a single shaft. A fluid coupling is provided between the engine and the turbocharger by the turbine using the energy of the engine exhaust-gas to drive the compressor. The compressor, in turn, draws in fresh air and, upon having its temperature reduced by an after-cooler, supplies compressed air to assist in driving the fired pistons of the engine cylinders. It is also known to direct a quantity of turbine exhaust-gas energy from the engine and combine it with the inlet airflow for assisting in driving all or a portion of the pistons. The inventor herein has recognized the disadvantages of known compound engines, such as the loss of fuel efficiency and the decrease in air quality.